投料顺序对动态硫化PP／EPDM性能影响及其机理的研究

针对ＰＰ降解在ＰＰ／ＥＰＤＭ动态硫化中对体系产生的不利影响。考察了四种不同投料顺序对ＰＰ／ＥＰＤＭ动态硫化物的冲击韧性，加工流动性，交联程度和断面形貌等宏观和微观性能，并进行了不同ＥＰＤＭ含量的动态硫化和非硫化ＰＰ／ＥＰＤＭ的性能比较。结果表明，优化投料顺序能实现对动态硫化体系中化学反应对象和化学反应程度的有效干预。     

基于主被动合作博弈的医患关系研究

针对我国医患关系日趋紧张,医患矛盾逐渐凸显这一问题,在对中国近五年医患事件进行分析的基础上,分别从信任程度、信息不对称程度、诊疗代价等多个视角出发,利用演化博弈理论和复制动态方程,构建了医患双方合作策略选择演化博弈模型,探究了影响医患关系演化的相关因素。研究表明:从长期来看,医患关系博弈系统存在两种演化路径:主动合作和被动合作;增大医患双方的信任程度,减小医患双方的信息不对称程度,降低医患双方合作成本,增大以政府为主导的仲裁机构对医患双方的奖励和惩罚都将会促使医患双方由被动合作转向主动合作。     

Optimizing constrained subtrees of trees

Given a treeG = (V, E) and a weight function defined on subsets of its nodes, we consider two associated problems. The first, called the rooted subtree problem, is to find a maximum weight subtree, with a specified root, from a given set of subtrees.The second problem, called the subtree packing problem, is to find a maximum weight packing of node disjoint subtrees chosen from a given set of subtrees, where the value of each subtree may depend on its root.We show that the complexity status of both problems is related, and that the subtree packing problem is polynomial if and only if each rooted subtree problem is polynomial. In addition we show that the convex hulls of the feasible solutions to both problems are related: the convex hull of solutions to the packing problem is given by pasting together the convex hulls of the rooted subtree problems.We examine in detail the case where the set of feasible subtrees rooted at nodei consists of all subtrees with at mostk nodes. For this case we derive valid inequalities, and specify the convex hull whenk 4.Research supported in part by Nato Collaborative Research Grant CRG 900281, Science Program SC1-CT91-620 of the EEC, and contract No 26 of the programme Pôle d'attraction interuniversitaire of the Belgian government.     

Simultaneous distillation-extraction and dynamic headspace methods in the gas chromatographic analysis of Parmesan cheese volatiles

Summary Dynamic headspace and simultaneous steam distillation-extraction techniques were used to isolate volatile components of Parmesan cheese. Identification of the substances was carried out by GC and GC-MS; 110 compounds were identified in the samples obtained using the headspace technique, 105 in the extracts; among them, about 50 compounds were isolated with both procedures. Mass spectral data showed evidence for a number of newly reported compounds such as 3-(methylthio)propanal, -tetradecalactone, 9-tetra-decenoic and 9-hexadecenoic acids. Mass spectra of some compounds are discussed and a comparison between the results obtained with the two sampling methods is given.     

Mass shifting roles of negative kernel mass in density estimation

f(x) is a univariate density in C ⁴ with bounded support. For any n and sufficiently small kernel bandwidths, the symmetric appendage of any negative mass, –U, to any smooth unimodal symmetric kernel of order p=2 shifts expected estimator mass from regions where f(x)>0 to regions where f(x)<0. For large n, the mean automatic kernel adaptation induced by –U is analyzed in the simplest MISE reduction scenario: The symmetric appendage of –U to the uniform kernel K(x, X) over MISE-optimal bandwidths reduces MISE by shifting K(x, X) mass asymmetrically across the observation X in the direction of decreasing |f(x)|.     

Optimality of a Threshold Policy in theM/M/ queue with repeated vacations

Consider anM/M/1 queueing system with server vacations where the server is turned off as soon as the queue gets empty. We assume that the vacation durations form a sequence of i.i.d. random variables with exponential distribution. At the end of a vacation period, the server may either be turned on if the queue is non empty or take another vacation. The following costs are incurred: a holding cost ofh per unit of time and per customer in the system and a fixed cost of each time the server is turned on. We show that there exists a threshold policy that minimizes the long-run average cost criterion. The approach we use was first proposed in Blanc et al. (1990) and enables us to determine explicitly the optimal threshold and the optimal long-run average cost in terms of the model parameters.     

Dimer asymmetry in superoxide dismutase studied by molecular dynamics simulation

Summary Molecular dynamics (MD) simulations of 100 ps have been carried out to study the active-site behaviour of the Cu,Zn superoxide dismutase dimer (SOD) in water. The active site of each subunit was monitored during the whole simulation by calculating the distances between functional residues and the catalytic copper. The results indicate that charge orientation is maintained at each active site but the solvent accessibility varies. Analysis of the MD simulation, carried out by using the atomic displacement covariance matrix, has shown a different intra-subunit correlation pattern for the two monomers and the presence of inter-subunit correlations. The MD simulation presented here indicates an asymmetry in the two active sites and different dynamic behaviour of the two SOD subunits.     

Bond-length fluctuations in transition-metal oxoperovskites

Bond-length fluctuations in transition-metal oxoperovskites may give rise to two-phase fluctuations in what appears to be a single phase to a diffraction experiment. Orbital disorder at Jahn-Teller ions results in bond-length fluctuations that give 3D-ferromagnetic, vibronic Mn(III)-O-Mn(III) superexchange interactions and allow disproportionation into Mn(IV) and Mn(II) in LaMnO₃; where orbitally ordered and disordered phases coexist, an external magnetic field stabilizes the orbitally disordered, ferromagnetic phase relative to the orbitally ordered, antiferromagnetic phase. Spin-lattice interactions in the paramagnetic phase of charge-transfer compounds give bond-length fluctuations arising from the semicovalent component of the superexchange interactions. At the crossover from localized to itinerant electronic behavior, the coexistence of two-phase fluctuations has been demonstrated in both the single-valent RNiO₃ family (R=rare-earth, A=alkaline-earth) and the mixed-valent R_0.5A_0.5MnO₃ perovskites. “Bad-metal” behavior is found to be associated with bond-length fluctuations.     

在"高聚物的结构与性能"课程中应该引入的几个新概念

在“高聚物的结构与性能”课程教学中，很有必要向学生介绍高分子科学近十几年来的发展，尤其是在高分子凝聚态基本物理问题上的研究成果以及相关的新概念、新知识，特别是我国学者的贡献。本文较为详细地讨论了近年来作者在教学中介绍的几个新概念，如：动态接触浓度、单链凝聚态、凝聚缠结等。     

Dynamic surface tension of micellar solutions studied by the maximum bubble pressure method. 1. Experiment

The effect of the micelles on the dynamic surface tension of micellar surfactant solutions is studied experimentally by means of the maximum bubble pressure method. Different frequencies of bubbling ranging approximately between 1 and 30 s^–1 are applied. The time dependence of the surface tension is calculated using a dead time correction. Water solutions of two types of surfactants with different concentrations are investigated: sodium dodecyl sulfate and nonylphenol polyglycol ether. The surface tension relaxes more quickly in the presence of micelles. The characteristic times of relaxation of the surface tension seem to be in the millisecond range. The time constants observed experimentally are explained in terms of the theory of surfactant diffusion affected by micellization kinetics.